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FreeBSD-EN-21:03.vnet                                           Errata Notice
                                                          The FreeBSD Project

Topic:          Panic when destroying VNET and epair simultaneously

Category:       core
Module:         kernel
Announced:      2021-01-29
Affects:        FreeBSD 12.1 and later.
Corrected:      2020-12-15 15:33:28 UTC (stable/12, 12.2-STABLE)
                2021-01-29 01:20:52 UTC (releng/12.2, 12.2-RELEASE-p3)
                2021-01-29 01:06:03 UTC (releng/12.1, 12.1-RELEASE-p13)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

VNET permits systems to be configured with multiple instances of the in-kernel
network stack.

The epair(4) interface provides a pair of virtual back-to-back connected
Ethernet interfaces.

II.  Problem Description

Insufficient locking in the kernel meant that destroying an epair and a vnet
jail at the same time often resulted in panics.

III. Impact

Users with root level access (or the PRIV_NET_IFCREATE privilege) can panic
the system.

IV.  Workaround

The panic can be avoided by ensuring that epair interfaces are fully destroyed
before the vnet jails containing them are destroyed.

Systems not using vnet jails are not affected.

V.   Solution

Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date and reboot.

Perform one of the following:

1) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for an errata update"

2) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-21:03/vnet.patch
# fetch https://security.FreeBSD.org/patches/EN-21:03/vnet.patch.asc
# gpg --verify vnet.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r368663
releng/12.2/                                                      r369172
releng/12.1/                                                      r369163
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=238870>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-21:03.vnet.asc>
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